Abstract: The ability to obtain neurons directly from the patients with neurological disorders will offer opportunities to study pathogenesis from the affected cells and develop novel therapeutic approaches. In hereditary neurological diseases, patient-specific neurons reprogrammed from non-neuronal cell types will harbor the same genetic mutation, thus offering valuable tools to study cell-autonomous pathology. For the disorders of somatic neurodegeneration, the isogenic, induced neurons may be used for cell replacement-based therapies. Most of current approaches towards deriving human individual-specific neurons have focused on transforming a differentiated cell type (for instance, dermal fibroblasts) to a pluripotent state and further differentiating them into neurons. This method requires forced expression of tumorigenic transcription factors that are highly expressed in embryonic stem cells. Moreover, differentiation of multipotent neural progenitors into specific subtypes of neurons is a difficult process to control. I have devised an alternative strategy of non-invasively obtaining neurons from adult human skin cells by converting their cell fate without going through pluripotent state (thus not requiring the expression of tumorigenic genes) and directly into post-mitotic neurons (direct reprogramming). I recently discovered that neuron-specific microRNAs (miR-9/9* and miR-124) could promote the switching of a non-neuronal cell fate into neurons when ectopically expressed with as few as one neural factor. The reprogramming efficiency was higher with more neural factors, and I devised a protocol in which miR-9/9* and -124 with neural factors, NeuroD2, ASCL1 and Myt1l generated neurons with cortical neuron-like characteristics. In this proposal, I will develop strategies to directly reprogram non-neuronal cells into various subtype-specific neurons. In developing tissue culture models of neurological diseases, it is important to obtain the type of neurons affected by the disease. Because the miR-9/9* and miR-124 are expressed pan-neuronally, I hypothesize that neuronal reprogramming can be customized for different subtypes of neurons by using transcription factors specific for the desired cell type in the background of miR-9/9*-124 expression. I will extend these studies to apply the direct reprogramming method in vivo from non-neuronal cells and hope to gain insights into possible restoration of the neuronal function lost in animal models of neuronal injury. Public Health Relevance: The ability to non-invasively obtain neurons from human individuals with neurological disorders will offer novel directions towards disease modeling and cell replacement-based therapeutic approaches. Here, we prose to devise methods to directly reprogram non-neuronal cell fates into subtype-specific neurons and develop in vivo application of this method in animal models of neuronal injury.